Extreme Leak Rate of Isolation Valve at TAQA Gas Storage, The Netherlands
Unplanned maintenance: Total plant shutdown to repair external gas leak
The TAQA Gas Storage, Bergermeer gas processing facilities are connected via a 2x8.5km 30″ pipe to the wellhead site. The 1st isolation valve on the processing facilities site was passing heavily, which made safe work on the 2nd valve (which had a broken stem seal) impossible. Greasing has been tried but failed to improve the situation. The only solution was to depressurize the whole pipeline system.
Valvetight was called to assist. After an assessment of the situation, it was decided to use the first valve as the first block. The second valve was of the SR (self-relieving) type, so only the upstream seat would have a sealing function anyway (the 2nd seat is pushed away from the ball when pressurized via the body cavity). It was decided that the work on the stem seal of the 2nd valve was equal to working on any piece of equipment just downstream of the 2nd blockvalve. WMS, LMRA and MoC were executed and the DBB-SAVER was connected to the bleed valve between both block valves.
As the leakage was very severe, it was decided to lower the pressure in the pipeline by producing gas with all wellhead headers closed, so overnight the pressure was lowered from 70 to 37 bar, which reduced the in-line leakage to a “manageable” 20 m3/min through the first block valve. The DBB-SAVER was equipped with a 2nd venturi in series which easily handles these leak rates and after the work permits were signed and Valvetight commenced their job, the leakage through the 2nd valve’s stem seal stopped. The DBB-SAVER created a safe work place within 30 minutes after Valvetight commenced, including connecting the DBB-SAVER to TAQA’s installation.
TAQA saved a significant amount of gas which otherwise had to be bled to the atmosphere. Besides, TAQA saved a couple of days of complete plant shutdown. Increased safety, plant up-time and prevention of gas emissions were all combined thanks to the application of the DBB-SAVER.
Saving 300.000m3 of NG and prevention of 4 days forced total plant shutdown